Conventionally, there has been proposed an apparatus, the main portion of which is shown in FIG. 1 as a magneto-optical recording apparatus which is capable of rewriting information by overwriting.
In FIG. 1, reference numeral 1 designates a magneto-optical disk, and in the present example, this magneto-optical disk 1 is formed by depositing a perpendicular magnetization layer 3 on a glass substrate 2 and this magneto-optical disk 1 can be rotated with a central axis 0 - 0' as the center.
Further, reference numeral 4 indicates an optical head section for irradiating a laser light LB on the perpendicular magnetization layer 3. In the present example, the optical head section 4 is provided with a semiconductor laser element 5 and a lens 6 and this optical head section 4 is arranged to be movable along the radial direction of the magneto-optical disk 1 maintaining a predetermined distance from the surface of the magneto-optical disk 1. In this case, the optical head section 4 is operative to locally irradiate the perpendicular magnetization layer 3 of the magneto-optical disk 1 with the laser light LB with a constant intensity continuously emitted from the semiconductor laser element 5 through the lens 6 so as to elevate the temperature on the irradiated part of the perpendicular magnetization layer 3 above the Curie point.
Reference numeral 7 designates an electromagnet for applying a magnetic field to he perpendicular magnetized film 3 of the magneto-optical disk 1. In the present example, the electromagnet 7 is placed facing the optical head section 4 with the magneto-optical disk 1 interposed therebetween, and the electromagnet 7 is arranged to be movable along the radial direction of the magneto-optical disk 1, associated with the optical head section 4.
Further in the present example, a magnetic field modulating circuit 8 is provided, the input side of this magnetic field modulating circuit 8 is connected with a recording signal input terminal 9 and the output side of this magnetic field modulating circuit 8 is connected with a coil 7A of the electromagnet 7. By the magnetic field modulating circuit 8, a current, the phase of which is inverted in response to recording signal supplied thereto through the record signal input terminal 9, for example, a current flowing in the direction of an arrow A is supplied to the coil 7A when the signal level of a recording signal is at a high level "1", and a current flowing in the direction of an arrow B is supplied to the coil 7A when the signal level of a record signal is at a low level "0", whereby the electromagnet 7 generates a magnetic field as indicated by an arrow X when the signal level of the recording signal is at the high level "1", and a magnetic field as indicated by an arrow Y when the signal level of the recording signal is at the low level "0". In this case, the magnetic field indicated by the arrow X and the magnetic field indicated by the arrow Y are directed opposite to each other, however, the intensities thereof are made equal to each other. If the intensities of the magnetic field indicated by the arrow X and the magnetic field indicated by the arrow Y are designated Hc and -Hc, respectively, in consideration of their directions, .vertline..+-.Hc.vertline. are respectively determined to be such an intensity that the magnetizing direction of the perpendicular magnetization layer 3 of the magneto-optical disk 1 can be directed in the direction of the respective magnetic fields.
In the present example of the magneto-optical recording apparatus thus constructed, when a recording signal, for example, as shown in FIG. 2A, is supplied to the magnetic field modulating circuit 8, the electromagnet 7 produces a magnetic field as shown in FIG. 2B, and this magnetic field is to be applied to the perpendicular magnetization layer 3 of the magneto-optical disk 1. In this case, since the perpendicular magnetization layer 3 of the magneto-optical disk 1 has been irradiated with the laser light LB with a constant intensity E which can elevate the temperature of the perpendicular magnetization layer 3 above the Curie point, as shown in FIG., 2C, there are consequently recorded recording patterns 10A, 10B . . . 10E as typically shown in FIG. 2D in a recording track 3A on the perpendicular magnetization layer 3 of the magneto-optical disk 1. Incidentally, the recording of + and - of this case respectively indicate the magne the upward direction (the direction indicated by the arrow X in FIG. 1) and in the downward direction (the direction indicated by the arrow Y in FIG. 1).
As described above, by the magneto-optical recording apparatus of the present example, a minute portion on the perpendicular magnetization layer 3 of the magneto-optical disk 1 is continuously heated above the Curie point with the laser light LB, the heated minute portion is moved, and when the temperature thereof becomes in the proximity of the Curie point, the portion in the proximity of the Curie point is magnetized in the direction of the magnetic field which is modulated in accordance with the recording signal. When the temperature is further lowered, the magnetization is maintained to thereby magneto-optically recording signals, taking a portion of a size smaller than that of the heated minute portion to be a unit. According to such the magneto-optical recording apparatus, regardless of any information recorded on the perpendicular magnetization layer 3 of the magneto-optical disk 1, it is possible to record new information by overwriting.
However, in the conventional magneto-optical recording apparatus as shown in FIG. 1, when the magnetic field which is applied to the perpendicular magnetization layer 3 of the magneto-optical disk 1 is inverted in its direction in accordance with the signal level of the recording signal, a definite time period t.sub.1 as shown in FIG. 2B is required. During the inverting time period t.sub.1, although the magnetic field with the intensity .vertline..+-.Hc.vertline., necessary for orientating the magnetization in the direction of the magnetic field, is not applied to the perpendicular magnetization layer 3, since it is continuously irradiated with the laser light LB with the constant intensity E, regions in which the noise level is increased to cause errors to easily occur during reproduction, that is, so-called noise-up regions 11A, 11B . . . 11E, as shown in FIG. 2D, occur in the recording track 3A corresponding to the magnetic field inverting time period t.sub.1, thereby incurring a disadvantage that high density recording cannot be satisfactorily carried out.